Delete unused --additional-apk-incremental test_runner.py flag

This flag doesn't exist, and so test_runner.py has been passing it
through as a chrome flag to tests :P

Change-Id: I562e5c62a9a3fa7caf4b7bdfd49713d0f21d7774
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1625837
Commit-Queue: Andrew Grieve <agrieve@chromium.org>
Commit-Queue: Eric Stevenson <estevenson@chromium.org>
Auto-Submit: Andrew Grieve <agrieve@chromium.org>
Reviewed-by: Eric Stevenson <estevenson@chromium.org>
Cr-Commit-Position: refs/heads/master@{#662822}

build/config/android/internal_rules.gni

@@ -810,8 +810,6 @@ template("test_runner_script") {
         executable_args += [
           "--additional-apk",
           "@WrappedPath(@FileArg($_rebased_build_config:deps_info:apk_path))",
-          "--additional-apk-incremental",
-          "@WrappedPath(@FileArg($_rebased_build_config:deps_info:incremental_apk_path))",
         ]
       }
     }